Problem: What do the following two equations represent? $-4x-5y = -4$ $16x+20y = 16$
Answer: Putting the first equation in $y = mx + b$ form gives: $-4x-5y = -4$ $-5y = 4x-4$ $y = -\dfrac{4}{5}x + \dfrac{4}{5}$ Putting the second equation in $y = mx + b$ form gives: $16x+20y = 16$ $20y = -16x+16$ $y = -\dfrac{4}{5}x + \dfrac{4}{5}$ The above equations turn into the same equation, so they represent equal lines.